Oracle Script to Update One Table's Field Based on Another Table

I'm sure this is a simple query but here goes ... I have two related tables A and B. One record in table A might have many related records in table B. If it does, I want to update one column in all of table B's related records with a specific value based on a value in Table A.

So, for example, if TABLEA.COLUMN3 = 123 then I want to update TABLEB.COLUMN5 values to 'ABC' in all related TABLEB records. Another example  --> if TABLEA.COLUMN1 = 456, then I want to update TABLEB.COLUMN5 values to 'DEF' in all related TABLEB records.

Something like (I know this isn't right):

update TABLEB
from TABLEA
set TABLEB.COLUMN5 = 'ABC'
where TABLEA.COLUMN3 = 123 and TABLEA.COLUMN1 = TABLEB.COLUMN2